The use of membranes for gas separations is widely known. The separation of gases by membranes requires the selection of specific materials which selectively permeate one gas composition preferentially to other gas compositions. Typically, separation of gas mixtures with membranes results in a reject gas or gas which does not permeate through the membrane as well as a permeate gas, one of which is of unacceptable value and therefore vented or used for low value end uses, such as combustion.
It is also known to supply large volume industrial gases such as hydrogen, helium, argon, methane, oxygen or nitrogen via pipeline from a major source of the industrial gas to one or more end users. Such pipeline industrial gas is generally of a very high quality, including pressure and purity, so as to suit the needs of most of the pipeline customers for the industrial gas. However, with the advent of industrial gas consumption by new applications in industry which require ultra high standards, it has become necessary to supply such new applications with pipeline volumes of industrial gases, which meet even higher purity standards than traditional quality industrial gas pipeline supplies provide.
Purification stations branching off of industrial gas pipelines have been known to be used, but these require capital intensive purification hardware and/or energy intensive pressurization or repressurization for appropriate processing.
U.S. Pat. No. 3,986,350 discloses a process for filtering hydrogen through a membrane for subsequently combustion.
U.S. Pat. No. 4,130,403 discloses a process for removing hydrogen sulfide and carbon dioxide from natural gas using a membrane.
U.S. Pat. No. 4,264,338 discloses a process wherein various reject streams are returned to a feed stream in a multiple membrane separation.
U.S. Pat. No. 4,374,657 discloses a process which includes a membrane for removal of hydrogen sulfide and carbon dioxide from an ethane and carbon dioxide stream.
U.S. Pat. No. 4,529,411 discloses a process for removing carbon dioxide from a hydrocarbon stream which contains residual carbon dioxide.
U.S. Pat. No. 4,597,777 discloses a membrane process wherein a reject methane-rich product is separated from a carbon dioxide and methane permeate, the latter of which is combusted.
U.S. Pat. No. 4,654,047 discloses a process wherein a hydrogen is removed as a permeate through a membrane from a feed gas stream and the reject gas is processed cryogenically to upgrade the hydrogen content in the reject gas, which is then recycled to the feed gas stream.
U.S. Pat. No. 4,690,695 discloses multiple membrane systems for recovering hydrogen from mixtures with methane.
U.S. Pat. No. 4,863,492 discloses a process wherein a permeate from a feed gas stream passes through a membrane, is further upgraded in a pressure swing absorption unit and the reject from the pressure swing absorption unit is recycled to the reject from the membrane.
The prior art has failed to suggest a solution to the problem of providing a low cost, higher purity sidestream gas product from a main product pipeline gas of lower, but still valuable purity level, while avoiding capital intensive elaborate apparatus or energy intensive processing. The present invention overcomes this problem as will be set forth in greater detail below.